Field of the Invention
The invention relates, in general, to gas analyzers and, in particular, to a new and useful exhalation air analysis device with a flow duct, through which the exhalation air of a tested person flows and with an analysis chamber in which the exhalation air has contact with a detector reacting to a component of the exhalation air and generating a metering signal.
For the analysis of human exhalation air, and in particular for the determination of the alcohol concentration in the exhalation air, analysis devices have been used for many years in addition to the known chemically operating test tubes, which use a detector reacting specifically to the concentration of the respective substance and generating a respective electrical output signal. Electro-chemical detectors are used in particular. Herein especially those detectors working on the basis of the coulometric metering principle have proven successful for alcohol analysis.
In such a metering process the concentration is not determined directly, but the amount of a species or substance which is transformed on the detector surface in a certain period of time. It is also called an absorption, process. The invention is related specifically to the use of detectors working according to the coulometric process or another absorption process.
In order to determine the concentration of the substance in the exhalation air by means of the amount metered, it is necessary to isolate a defined volume of the exhalation air for testing. For this purpose the respective analysis devices have therefore an analysis chamber, which is usually connected to the flow duct through which the ventilation air of the test person flows.
U.S. Pat. No. 3,854,320 describes a ventilation air analysis device, in which the analysis chamber is a part of the flow duct which is arranged permanently in the path of the ventilation air. The detector is arranged in the analysis chamber, but it is at first covered by a cap during the breathing process. Only toward the end of the breathing process is the exhalation air flow interrupted and the detector uncovered by the lifting of the cap, so that the metering or measuring can take place.
In the analysis device described in German patent No. A-29-44 444 the analysis chamber is connected to the flow duct by means of a connecting line. At the desired moment a sample is sucked from the flow duct into the analysis chamber. For this purpose a pumping device connected to the analysis chamber comprising an element which moves in a piston-like manner in a respective housing, is provided.